That's not accurate -- the subnet mask is different from the IP address, and I can happily share my iTunes music from a computer with IP address 192.168.0.12 to a computer with an IP address of 192.168.5.100. The subnet is not determined by the first three triplets of the IP address.
The actual subnet of my network, though, is 255.255.255.0 -- completely different from the IP address.
In terms of music, start thinking of your iPod as a "one-way" music device -- meaning, music goes onto the iPod and doesn't come back off of it. The sooner you start thinking this way (which is the intuitive, Apple-supported way) the sooner you'll enjoy the iPod much, much more. It's going to be nothing but frustration if you try and use the device counter-intuitively, much like trying to drive your car from the back seat will only leave you frustrated -- it's counter-intuitive.
Short answer: if you wanna share music through iTunes, do it through iTunes. The iPod and it's music library are not an external hard drive -- if you want to share files from the iPod, copy the files to the iPod in disk mode and share from there -- with the side effect being that you can't listen to these music files via the iPod.